Biodegradation of non-desorbable naphthalene in soils

The degradation of naphthalene was studied in soil-slurry systems, and a qu antitative model was developed to evaluate the bioavailability of sorbed-ph ase contaminant. Four soils with different organic matter contents were use d as sorbents. Two naphthalene-degrading organisms, Pseudomonas putida G7 a nd NCIB 9816-4, were also selected. Sorption isotherms and single and serie s dilution desorption studies were conducted to evaluate distribution coeff icients, desorption parameters, and the amount of non-desorbable naphthalen e. Biodegradation kinetics were measured in soil extract solutions and rate parameters estimated. Bioavailability assays involved establishing sorptio n equilibrium, inoculating the systems with organisms, and measuring naphth alene concentrations in both sorbed and dissolved phases over time. For all four soils, the sorption isotherms were linear, and desorption could be de scribed by a model involving three types of sites: equilibrium, nonequilibr ium, and non-desorption. Enhanced bioavailability, as evidenced by faster t han expected degradation rates based on liquid-phase concentrations, were o bserved in soils with the higher sorption distribution coefficients. These observations could be described using model formulations that included soli d-phase degradation. In all soils studied, degradation of non-desorbable na phthalene was observed.